minor symfony#4968 Fix typo (ifdattic)

This PR was merged into the 2.3 branch.

Discussion
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Fix typo

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.3
| Fixed tickets |

Commits
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34b38f3 Fix typo

Author: wouterj

book/validation.rst

@@ -1236,7 +1236,7 @@ By calling ``validateValue`` on the validator, you can pass in a raw value and
 the constraint object that you want to validate that value against. A full
 list of the available constraints - as well as the full class name for each
 constraint - is available in the :doc:`constraints reference </reference/constraints>`
-section .
+section.
 
 The ``validateValue`` method returns a :class:`Symfony\\Component\\Validator\\ConstraintViolationList`
 object, which acts just like an array of errors. Each error in the collection